20 lb radiator cap? 5.3 ls swap

[robert_63]

I have a question, I'm using my stock radiator for my 85. I bought a new cap. A 13 pr 16 lb I believe, and it wouldn't seal to the radiator it wouldn't pressure up just blow out . I stepped up to a 20 lp cap just to try it and it sealed like it supposed to, what I'm asking is. Is this too much? I don't know anything about the lb rating of a radiator cap or the system pressures required, all I know is the 13 lb cap wouldn't seal off and I figured it wouldn't work